The importance of CD8+ T lymphocytes in human immunity against many viral diseases and tumors has been well established. Dendritic cells (DCs) have emerged as the premier antigen presenting cell (APC) the initiation of immune responses. In fact, the targeting of DCs in vivo and in ex vivo procedures for antigen presentation of tumor and viral vaccine candidates is being extensively investigated. Thus, a better understanding of the molecular interactions between human DCs and CD8+ T cells during primary stimulation is highly desirable. TO this end, we have chosen to study the primary stimulation of human CD8+ T cells with allogeneic DCs. This system has a number of advantages including the HLA class restricted stimulation of sufficient numbers of CD8+ T cells to allow detection and the availability of both immature DCs (iDCs) and mature DCs (mDCs) from donor PBMC cultures for use as APCs. Aim 1. The ability of allogeneic APCs, in particular iDCs and mDCs, to stimulate primary CD8 + T lymphocyte responses will be both qualitatively and quantitatively assessed. Four different criteria will evaluated: (a) up-regulation (CD25, CD69, CD44, CD45RO) and down-regulation of T cell markers (CD45RA, CD62L), (b) proliferation, and the differentiation of (c) cytotoxic responses and (d) TC1 (IFN-gamma and IL-2) vs. TC2 (IL-4 and IL-5) cytokine production profiles. Aim 2. The factors on or secreted by allogeneic iDCs and mDCs involved in human CD8+ T lymphocyte activation and differentiation, as measured by the above four criteria, will be dissected. (a) The roles of the costimulatory molecules, CD8O and CD86, expressed on allogeneic DCs in the activation and differentiation of the CD8+ T cells will be examined. (b) The role of IL-12 production by allogeneic DCs on activation and differentiation of CD8+ T cells will be evaluated. (c) The effect of the Th2/TC2 cytokines, IL-4 and IL-10, in allogeneic stimulation of the CD8+ T cells will be determined.